Field of the Invention:
The present invention relates to compositions useful in treating and coating metallic substrates so as to make them corrosion resistant. The invention also relates to a method of treating or coating metallic substrates and to the treated and coated substrates.
Brief Description of the Prior Art:
It is known in the art to prepare corrosion-resistant substrates by applying to the substrates compositions comprising metallic ions. Eminent in this art are phosphatizing treating compositions. Examples of the phosphatizing treating compositions are those containing iron phosphate, zinc phosphate or zinc calcium phosphate.
Although the metallic treating compositions are employed on many industrial lines, they, nonetheless, have certain disadvantages. They are expensive; besides the cost of the chemicals, a considerable capital investment is required for equipment. Also, the process for using these treating compositions results in pollution, the cleaning of which adds to the overall cost of operations.
The present invention employs tannin-epoxy reaction products to provide relatively inexpensive, yet highly effective means of producing corrosion-resistant substrates. Although tannins, by themselves, have been employed as corrosion inhibitors, they have been found to be lacking in substrate adhesion. Their reaction products are difficult to prepare; once prepared, they have been found to be either gelled and, therefore, undesirable for application to substrates, or rather unstable, upon storage. The novel tannin-epoxy reaction products are ungelled, stable and have excellent properties of substrate and intercoat adhesion and corrosion resistance.